Method of coating the surface of an inorganic substrate with an organic material and the product obtained

ABSTRACT

A method of coating the surface of an inorganic substrate of glass, silicon dioxide, ceramics or carbon, which method comprises a step of cleaning the surface of the substrate by subjecting the surface to a reducing gas plasma and forming a first layer on the substrate surface using a plasma enhanced polymerization process employing one or more monomers comprising monomers with a sufficient low molecular weight for them to be in their gaseous state in the gas plasma, selected from the group consisting of C 1 -C 16  alkanes, C 2 -C 16  alkenes, C 2 -C 16  alkynes, styrene, aromatic monomers of styrene compounds, monomers of vinyl- and acrylate-compounds.

The present invention relates to a method for coating the surface of aninorganic substrate of glass or carbon with an organic material and theproduct obtained.

Coating of glass or carbon substrates with organic material is a verydifficult process. To obtain sufficient binding strength between thecoating material and the substrate material it is necessary to clean thesurface of the substrate before coating. This cleaning is usually achemical treatment, e.g. with organic solvents, to remove impurities.Even after the cleaning process the bonding between the organicmolecules of the coating and the inorganic surface of the substrate hasdifficulties in resisting especially strong basic and strong ionic(salt) environments. The problem is well known from adhering of polymersto glass, where the polymer-coatings have a tendency to de-bind from theglass substrate and loose their ability to fulfil their purpose.

Several attempts have been made to avoid the above-mentioned problemsand one solution is the use of plasma technology.

U.S. Pat. No. 5,061,567 discloses a coated glass substrate and themaking of the same. A glass substrate is coated with an organomineralfilm in a plasma process. The purpose of the coating is primarily toimprove the optical properties of the glass and the coated glasssubstrate does not have any properties to resist the influence ofenvironments with e.g. high pH values.

Because of the difficulties in providing coatings on substrates of glassor carbon which do not have a tendency to de-bind from the substrate,there is a need for a method for coating surfaces of glass or carbonwhich will result in strong and durable bonding between the coating andthe surface of the glass or carbon, even when exposed to very harshenvironments e.g. with high pH values.

It has now surprisingly appeared that the above-mentioned needs can bemet by the present invention. The invention provides a method by which asurface of an inorganic substrate, such as glass or carbon, can becoated with organic material, and where the bonding between thesubstrate and the coating is extremely strong and is able to resistharsh chemical environments e.g. with high pH values.

The invention also provides a method which is more environment-friendlythan the known methods, as no organic solvents are used in the method.Furthermore, the method according to the invention is relatively cheapand can be performed as a continuous process in one reaction chamber.

Furthermore, the invention provides a coated inorganic substrate with avery wear-resistant, strong and long lasting organic coating.

The method according to the invention and the coated substrate obtainedby the method are defined in the claims.

The method according to the invention provides substrates coated withorganic material that are very suitable for use in aggressiveenvironments with e.g. high pH values.

The coating is very strong and has only little tendency to de-bind fromthe substrate.

Furthermore, the method provides substrates coated with an organicmaterial which has appeared to be very suitable for use in biochemicalprocesses. Further, the coated substrate provides good basis forvulcanising.

The method of coating the surface of an inorganic substrate of glass,ceramics or carbon according to the invention comprises the steps of

i) cleaning the surface of the substrate by subjecting the surface to areducing gas plasma,

ii) activating the surface by generating radicals on the surface of thesubstrate by subjecting the surface to a reducing gas plasma and forminga first layer on the substrate surface using a plasma enhancedpolymerization process employing one or more monomers comprisingmonomers with a sufficient low molecular weight for them to be in theirgaseous state in the gas plasma, selected from the group consisting ofC₁-C₁₆ alkanes, C₂-C₁₆ alkenes, C₂-C₁₆ alkynes, C₂-C₁₆ alkynes, styrene,aromatic monomers of styrene compounds, monomers of vinyl- andacrylate-compounds.

In a preferred embodiment of the method according to the invention themonomers are selected from the group consisting of acethylene, ethane,ethylene, hexane, hexene, 1-hexene, 3-methyl-1-hexene, 1,4-hexadiene,hexyne, 1-hexyne, methylacrylate, styrene and vinylpyrolidone.

In order to secure that the monomers are able to be in their gaseousstate in the plasma it is preferred that the monomers have a molecularweight up to 350.

In the cleaning step it is important that the reducing gas issubstantially free of oxygen and preferably the reducing gas should beable to remove the major part or more preferably substantially all ofthe oxygen present at the surface of the substrate.

In a preferred embodiment or the method according to the invention thereducing gas is H₂, NH₃, B₂H₄ or F₂ or a mixture of H₂, NH₃, B₂H₄, or F₂and a inert gas, and preferably the mixture is a mixture of H₂ andargon.

In a preferred embodiment the substrate is coated with two layers oforganic material. By use of this method including two layers of organicmaterial a substrate having particular good properties for immobilizingbiomolecules, vulcanising and/or adhering onto may be obtained. Thisembodiment of the method according to invention may e.g. be carried outby subjecting the coated substrate to a plasma enhanced polymerisationof monomers selected from the group consisting of vinylpyrolidone,acrylonitrile, glycidylmatacrylate, methacrylacid-anhydride,methyl-benzaldehyde and other vinyl or acryl containing monomers.

To avoid any contact with the oxygen of the atmosphere and to make theprocess as less complicated as possible a preferred embodiment of themethod according to invention is that the method is executedsubsequently in one chamber and preferably the method is executed as acontinuous process.

As a precaution to prevent contact between oxygen and the substrate tobe treated it is preferred that the atmosphere in said chamber at anystep in the method is inert and/or reducing.

To optimize the conditions for the method according to invention it ispreferred that the pressure is 0.01 to 1.0 mbar while the method iscarried out, more preferably 0.04 to 0.4 mbar.

It is further preferred that the substrate is exposed to plasma withreducing gas from 1 to 3600 seconds, more preferably from 10 to 300seconds and preferably the substrate is exposed to plasma-polymerisationfrom 1 to 6000 seconds, more preferably from 10 to 120 seconds.

In preferred embodiments of the method according to the invention thestep i) comprises the generation of radicals by use of gas plasmagenerated by excitation of the gas in an alternating current (AC), adirect current (DC), low frequency (LF), audio frequency (AF), radiofrequency (RF) or microwave generated electric field. Of course, anyother suitable source for generating plasma may be used according withthe invention.

In a first preferred embodiment of the method according to theinvention, the inorganic substrate is glass or glass fibers.

In a second preferred embodiment of the method according to theinvention, the inorganic substrate is silicon dioxide.

In a third preferred embodiment of the method according to theinvention, the inorganic substrate is ceramic or ceramic fibers.

In a fourth preferred embodiment of the method according to theinvention, the inorganic substrate is a carbon or carbon fibers.

The invention also comprises a coated inorganic substrate obtained bythe method described above.

The invention may be carried out in any known type of equipment forcarrying out the process of generating of plasma for coating purposese.g. a 3-phase plasma chamber is very suitable.

The invention shall now be explained in further details with referenceto the examples. The examples are only meant to illustrate specificembodiments of the invention and should not in any way be considered tobe a limitation of the scope of the invention, as the skilled personwould be able to carry out the invention in may other ways.

EXAMPLE 1

A glass slide having a dimension of 2.5×7 cm was placed in a 12 litre3-phase plasma chamber. The pressure in the chamber was lowered to 0.08mbar and a mixture of argon (10 sccm) and hydrogen (5 sccm) was led tothe chamber.

A plasma of 10 W/litre was started. After 60 seconds the argon supplywas stopped and the hydrogen flow was increased to 15 sccm. Afteranother 60 seconds styrene was led to the chamber with 10 scam,immediately after the flow of hydrogen was stopped.

When 20 seconds had passed with flow of styrene, the effect was loweredto 2 W/litre. After 60 seconds with flow styrene, a flow ofmetacrylacid-anhydride was led to the chamber, and hereafter the styreneflow was stopped. The polymerisation of metacrylacid-anhydride wascontinued for 60 seconds.

The surface of the glass slide was used for binding DNA-oligomers, witha primary amine in the 3′-end. During the use of the bonded DNA, thesurface of the glass slide was exposed to environments having a pH valueup to 11.

EXAMPLE 2

Chopped glass fibres were placed in an 80 litres 3-phase plasma chamber.The chamber was designed, so the fibres moved from one end of the plasmato the other end and in such a way that the pumping was in the middle ofthe chamber. A flow of hydrogen was led to the end from which end thefibres were moving, and monomer was led to the other end.

During this process the pressure was 0.1 mbar, the flow of hydrogen was30 sccm and the flow of monomer acethylene was 30 sccm. The plasma hadan effect of 8 W/litre.

The starting velocity of the fibres was set so that the 5, fibres werein the hydrogen area in 90 seconds and in the acethylene area for 90seconds.

The fibres were used as reinforcement in rubber. The coating ofacethylene results in a large amount of dopple bindings in the surface,which are very suitable for reaction with a rubber matrix in the processof vulcanisation.

EXAMPLE 3

The Example relates to silicon wafers. When silicon wafers are exposedto atmospheric air, a silicon dioxide glass layer is formed on the wafersurface.

Binding organic compounds to this silicon dioxide glass is difficult, inparticular because a lot of process steps in the known chip technologyinvolve as well high pH as organic solvents.

4″ wafers were placed in a 250 litre 3-phase plasma chamber. Thepressure in the chamber was lowered to 0.05 mbar and a mixture of argon(20 sccm) and hydrogen (10 sccm) was led to the chamber.

A plasma of 2.5 W/litre was started. After 120 seconds the argon supplywas cut of and the hydrogen flow was increased to 25 sccm. After another120 seconds hexene was led to the chamber with a flow of 50 sccm,immediately after the flow of hydrogen was stopped.

After 30 seconds had passed with hexane flow, the plasma effect wasreduced to 1.5 W/litre and the plasma polymerisation continued foranother 30 seconds.

The resulting wafers were tested in different environments. Thehexane/wafer binding was resistant to NaOH solution at pH 14,acetone/ultrasound and heating up to 90° C.

1-17. (canceled)
 18. A method of coating at least one surface of aninorganic substrate comprising: i) cleaning the surface by subjectingthe surface to a first reducing gas plasma, ii) activating the surfaceby generating radicals on the surface by subjecting the surface to asecond reducing gas plasma and forming a first layer on the surfaceusing a plasma enhanced polymerization process comprising at least onemonomer with a sufficiently low molecular weight for the monomer to bein a gaseous state in the gas plasma, wherein said at least one monomeris chosen from C₁-C₁₆ alkanes, C₂-C₁₆ alkenes, C₂-C₁₆ alkynes, styrene,aromatic monomers of styrene compounds, and monomers of vinyl- andacrylate-compounds, wherein said inorganic substrate comprises glass,silicon dioxide, ceramics or carbon.
 19. The method of claim 18, whereinthe first reducing gas plasma and the second reducing gas plasma are thesame reducing gas plasma.
 20. The method according to claim 18, whereinsaid at least one monomer is chosen from acetylene, ethane, ethylene,hexane, hexene, 1-hexene, 3-methyl-1-hexene, 1,4-hexadiene, hexyne,1-hexyne, methylacrylate, styrene and vinylpyrolidone.
 21. The methodaccording to claim 18, wherein said at least one monomer has a molecularweight less than or equal to
 350. 22. The method according to claim 18,wherein the reducing gas plasma is reducing gas chosen from H₂, NH₃,B₂H₄, and F₂ or a mixture of reducing gas chosen from H₂, NH₃, B₂H₄, andF₂ and an inert gas.
 23. The method according to claim 18, wherein thereducing gas plasma is mixture of H₂ and argon.
 24. The method accordingto claim 18, wherein the inorganic substrate is further coated with asecond layer comprising subjecting the coated surface to a plasmaenhanced polymerization process comprising at least one monomer chosenfrom vinylpyrolidone, acrylonitrile, glycidylmethacrylate,methacrylacid-anhydride, methylbenzaldehyde and other vinyl or acrylcontaining monomers.
 25. The method according claim 18, wherein the stepof cleaning and the step of activating is executed sequentially in onechamber.
 26. The method according to claim 18, wherein the step ofcleaning and the step of activating is executed as a continuous process.27. The method according to claim 25, wherein the one chamber at anystep in the method has an atmosphere that is inert and/or reducing. 28.The method according to claim 18, wherein the method is practiced at apressure is 0.01 to 1.0 mbar.
 29. The method according to claim 28,wherein the method is practiced at pressure 0.04 to 0.4 mbar.
 30. Themethod according to claims 18, wherein the inorganic substrate isexposed to the first and/or second reducing gas plasma for a timeranging from 1 to 3600 seconds.
 31. The method according to claim 30,wherein the inorganic substrate is exposed to the first and/or secondreducing gas plasma for a time ranging from 10 to 300 seconds.
 32. Themethod according to claim 18, wherein the inorganic substrate is exposedto the plasma enhanced polymerisation process for 1 to 6000 seconds. 33.The method according to claim 32, wherein the inorganic substrate isexposed to the plasma enhanced polymerisation process for 10 to 120seconds.
 34. The method according to claim 18, wherein the step i)comprises generation of radicals by use of gas plasma generated byexcitation of a gas in an alternating current (AC), a direct current(DC), low frequency (LF), audio frequency (AF), radio frequency (RF) ormicrowave generated electric field.
 35. The method according to claim18, wherein the inorganic substrate is glass or glass fibers.
 36. Themethod according to claim 18, wherein the inorganic substrate is silicondioxide.
 37. The method according to claim 18, wherein the inorganicsubstrate is ceramic or ceramic fibers.
 38. The method according toclaim 18, wherein the inorganic substrate is carbon or carbon fibers.39. A coated inorganic substrate obtained by coating at least onesurface of the inorganic substrate by a method comprising: i) cleaningthe surface by subjecting the surface to a first reducing gas plasma,ii) activating the surface by generating radicals on the surface bysubjecting the surface to a second reducing gas plasma and forming afirst layer on the surface using a plasma enhanced polymerizationprocess comprising at least one monomer with a sufficiently lowmolecular weight for the monomer to be in a gaseous state in the gasplasma, wherein said at least one monomer is chosen from C₁-C₁₆ alkanes,C₂-C₁₆ alkenes, C₂-C₁₆ alkynes, styrene, aromatic monomers of styrenecompounds, and monomers of vinyl- and acrylate-compounds, wherein saidinorganic substrate comprises glass, silicon dioxide, ceramics orcarbon.